LUX-ZEPLIN (LZ) is a second-generation direct dark matter experiment with spin-independent WIMP-nucleon scattering sensitivity above $${1.4 \times 10^{-48}}\, {\hbox {cm}}^{2}$$
1.4
×
10
-
48
cm
2
for a WIMP mass of $${40}\, \hbox {GeV}/{\hbox {c}}^{2}$$
40
GeV
/
c
2
and a $${1000}\, \hbox {days}$$
1000
days
exposure. LZ achieves this sensitivity through a combination of a large $${5.6}\, \hbox {t}$$
5.6
t
fiducial volume, active inner and outer veto systems, and radio-pure construction using materials with inherently low radioactivity content. The LZ collaboration performed an extensive radioassay campaign over a period of six years to inform material selection for construction and provide an input to the experimental background model against which any possible signal excess may be evaluated. The campaign and its results are described in this paper. We present assays of dust and radon daughters depositing on the surface of components as well as cleanliness controls necessary to maintain background expectations through detector construction and assembly. Finally, examples from the campaign to highlight fixed contaminant radioassays for the LZ photomultiplier tubes, quality control and quality assurance procedures through fabrication, radon emanation measurements of major sub-systems, and bespoke detector systems to assay scintillator are presented.
The secondary electron emission coefficient γ of a MgO protective layer with various crystallinities has
been successfully measured by the γ-focused ion beam system with complete
elimination of the charge accumulation problem by scanning-area adjustment techniques. It is found that the (111) surface
has the highest γ from 0.14 to 0.26 in comparison with the other films with (200) and (220)
crystallinities for operating
Ne+ ions, while ranged from 0.03 to 0.24 for Ar+ ions, under operating ion energies
from 50 eV to 500 eV throughout this experiment.
These observations explain why the (111) crystallinity
of the MgO protective layer plays an important role in lowering the firing voltages in AC plasma display panel
compared to the films with other crystallinities.
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